The present invention relates to a viewing system and relates particularly, but not exclusively, to a panoramic sight for a military vehicle such as a tank.
Panoramic sights fitted to tanks enable the tank crew, under armour, to view the environment and to fulfil the functions of surveillance, target acquisition and target engagement. Viewing can be direct viewing i.e. by the human eye, or indirect viewing i.e. by a piece of apparatus such as a thermal imager or image intensifier. Furthermore, the viewing may be daylight viewing of optical radiation in the visible waveband or may involve thermal imaging of optical radiation in the infra-red waveband. It is also likely to be desirable to include laser range finding apparatus in the viewing system.
A known panoramic sight is shown in FIG. 1a. The panoramic sight is for direct daylight viewing and is indicated generally at 10 and comprises an objective window 12, an elevation mirror 14, an azimuth mirror 15, a system 16 for effecting field of view or magnification changes, a fixed mirror 18, a derotation prism 20, a telescope 22 and an exit pupil 24.
The elevation mirror 14 is servo driven and/or stabilised in the elevation axis over 90.degree. and the objective window 12 is connected to the elevation mirror so that these move together mounted on bearings (not shown). Thus, the size of the objective window 12 does not restrict the field of view in elevation. The objective window 12, the elevation mirror 14 and the azimuth mirror 15 are armour protected but above armour level and are collectively mounted on a bearing (not shown) to allow a servo drive and/or stabilisation to be achieved in the azimuth axis over 360.degree.. Below armour level, optical radiation from the field-of-view passes through the magnification changer 16 and is reflected by the fixed mirror 18 into the derotation prism 20 which is necessary to correct the image rotation which is introduced by both the elevational and the azimuthal angular movement.